Optical waveguides are extremely sensitive to surface and other interface imperfections which can cause scattering. Plasma processing of materials can cause residual plasma damage, which results in surface roughness and scattering.
Planar optical waveguides often require thick layers (1–20 microns thick) to be compatible with optical fiber dimensions, with typical core dimensions of 8–10 microns. However, these typically thicker layers cause critical process issues in fabricating waveguide devices. For example, the planarity, flatness and surface smoothness of a waveguide, which are the most critical of parameters that determine scattering loss of the waveguide, deteriorate with excessive topography during planarization and over-etching respectively. The problems become apparent when the device fabrication process requires the integration of more than one waveguide core, where the integrated waveguide cores are of different dimensions or are not coplanar. In the case where the waveguide core dimensions are different, planarization and mechanisms to protect the top surface of at least one of the waveguides during etch will be needed.
U.S. Pat. No. 5,199,092 to Stegmueller describes an optical waveguide device.
U.S. Pat. No. 4,954,459 to Avanzino et al. describes a planarization method using a sacrificial layer.
U.S. Pat. No. 5,510,652 to Burke et al. describes a chemical mechanical polishing (CMP) method using differing polish rates.
U.S. Pat. Nos. 5,863,828 to Snyder and 5,851,899 to Weigand describe planarization methods using both etching and CMP.
U.S. Pat. No. 6,258,711 to Laursen describes a CMP process with a sacrificial layer that polishes at a different rate than the fill layer to be planarized.
The Christian Laurent-Lund et al. article entitled “PECVD Grown Multiple Core Planar Waveguides with Extremely Low Interface Reflections and Losses”; IEEE Photonics Technology Letters, Vol. 10, No 10, pages 1431 to 1433; October, 1998 discloses a method of optical waveguide device fabrication using planarization by reverse masking and precise etching.